Ok, just got the Fireball and spent a couple hours with it. A/Bed it to the Archon as well as a couple other amps in my collection.
First impression, absolute monster! Lead channel - gain for days, and then some more. A dark amp indeed, but not limiting in the sense that cranking the treble really balances out the tone. Very aggressive voicing, tight and punchy, and easy to play. Quite compressed, but manageable with the gain at lower settings (which doesn't mean low gain hah!) Tons of low end on tap. Very thick sound overall, and above all else absolutely brutal. Great master volume! This amp is pretty much ideal for bedroom jamming.
Even so, the tone was a bit thick for my tastes...then I put an EQ in the loop and wow, it made all the difference. Pull some out in the 250 range, and add a bit more in the 1k - 4k to taste. It makes me wonder if all the players saying they couldn't get it to cut ever tried an EQ in the loop? Really no boundaries with this strategy minus the amp's inherent voicing.
Comparing to the Archon 100 - Overall, these two amps are more similar than different. The Archon is a bit smoother, and a touch less aggressively voiced. Similar amounts of gain (ie over the top if you want), but Fireball has even more and reminded me of the 5153 in that department. I'll give a nod to the Fireball for modern brutality, and a nod to the Archon for a bit better clarity under gain. Both amps are very tight, but with a nod to the Fireball in this department. I found the Fireball's cleans to be excellent - better than a 5153, but nod to the Archon. The Archon has a bit more versatility with two independent EQ's, but the Fireball has the built-in noise gate that worked beautifully. It's too early to decide which one I like better...the Fireball is just fun on a hilarious level. No boost or noise gate needed, tons of saturated, tight riffing to be had at whatever volume you choose. Makes me giggle. Throw an EQ in the loop and you can get a handful of usable tones. I agree it is bordering on the one trick pony, but again there are at least several awesome tones to be found in there, and the clean channel is no slouch.
Now I will say that I A/Bed it to my H&K Triamp Mk3. Not an apples to apples comparison in terms of price, but I have been really curious to compare these two German heads in the high gain department. The Triamp can get very close to the Fireball with some tweaking, and has crazy amounts of features, so it may not make sense to keep both. Anyways enough typing, gonna go back to chugging on the ENGL some more!!